Research on visuomotor control has yielded extensive evidence that the sensorimotor system strives to minimize intrinsic costs such as energy expenditure, jerk, or muscle stress. Traditionally studies concentrated on arm movements in simplified environments in which failure to meet the sole task demand (that the hand reach the target) had no important consequences for the subjects. Thus these findings cannot necessarily be extrapolated to visually guided movements under natural, more complex conditions in which motor errors have context-dependent extrinsic costs. The broad, long-term objective of the proposed research is to characterize how the human visuomotor system represents extrinsic costs in movement planning, and to investigate whether the systematic manipulation of extrinsic costs can be used for the shaping of desirable motor behavior in the rehabilitation of patients with motor deficits. The proposed project will introduce undergraduate students to research in visuomotor control, computational modeling and clinical application. Specific Aim 1: To describe the effect of extrinsic cost variation on the endpoint and trajectory of arm movements of normal human subjects. Subjects will receive objective, monetary penalties/rewards for contacting virtual obstacles/targets whose color will represent their associated extrinsic cost. Investigating how movement parameters change as a function of extrinsic cost will allow for computational models of how the visuomotor system represents such costs in motor planning. Specific Aim 2: To conduct a small pilot study to examine the effect of extrinsic cost variation on the movement trajectory of stroke patients. The ultimate goal of this part of the project is to assess whether this method of cost manipulation can be developed as an approach to motor rehabilitation. Stroke patients appear to develop long-term motor abnormalities as a result of operant conditioning, such that the extrinsic cost manipulations employed here might be developed as a method to retrain patients' motor patterns. Through this pilot study it will be possible to assess the feasibility of developing the experimental approach into such a method, and to develop parameters for a future study in which its effectiveness will be tested.